1. Field of the Invention
Apparatuses and devices consistent with the present invention relate to lamps and, more particularly, to lamps that use light emitting diodes (LEDs) as a light source and/or use light guide plates.
2. Description of Related Art
Lamps employing LED elements as a light source have been proposed as lamps for vehicles in recent years. When compared with incandescent lamps, the LED element is advantageous in reducing the consumed power. However, since the output angle at which light is outputted from the LED element is small, when LED elements are used for a vehicle lamp, the LED elements need to be arranged so as to increase the light emitting area of the lamp.
For example, a related art lamp described in Japanese Patent Unexamined Publication JP-A-2001-297609 includes a substantially circular reflector which has first and second reflecting surfaces for reflecting sequentially light emitted from LED elements. In this lamp, the light reflected on the first reflecting surface advances in a radial direction which is perpendicular to an optical axis, and the light so reflected is reflected by the second reflecting surface towards an opposite direction of the emitting optical axis, and then, the light is projected to a front side of the lamp. In this way, the light from the LED elements is made reflected in the radial direction by the first reflecting surface, the area where light is reflected from the second reflecting surface is increased, and light emitting area of the lamp as a whole is increased.
Further, in a related art lamp described in Japanese Patent Unexamined Publication JP-A-2003-59313, a reflector having a reflecting surface which is approximately a flat plane is arranged so as to face to a front side of the lamp while being tilted slightly downwards, and LED elements are arranged in a position lying directly underneath the reflecting surface.
In this lamp, the light emitted from the LED elements is made into a parallel beam by a Fresnel lens, and the parallel beam is projected onto the reflecting surface of the reflector, and the light reflected by the reflector is projected towards the front of the lamp. In this configuration, since light emitted from the LED elements can be projected onto almost the whole surface area of the reflecting surface, the lamp can be configured to have a wide light emitting area which corresponds to the area of the reflecting surface.
In this way, the related art lamps of JP-A-2001-297609 and JP-A-2003-59313 are advantageous in increasing the light illuminating area, compared with a case where light emitted from the LED elements is simply outputted from the lamp.
However, in the related art lamp described in JP-A-2001-297609, since the first reflecting surface is made in a substantially circular conical shape so that light from the LEDs is reflected in the radial direction in the form of the parallel beam, a light distribution pattern of the lamp to be formed becomes a substantially circular light distribution pattern. Thus, there is a disadvantage in that it becomes difficult to make an area close to the center function as a light emitting surface. In view of this disadvantage, in JP-A-2001-297609, separated LED elements or first and second reflecting surfaces for illuminating the central area are required, and accordingly, the resulting construction is complex. In addition, in the related art lamp described in JP-A-2001-297609, since the light emitting surface of the lamp is limited to the area where the second reflecting surface resides, that is, a plane (a two-dimensional plane) which is orthogonal to the optical axis where the light reflected on the first reflecting area resides, there is a is advantage in that it becomes difficult to apply the technique described in the JP-A-2001-297609 to, for example, an automotive lamp in which a horizontal light distribution range is made wider than a vertical light distribution range and in which the light emitting surface is curved vertically and horizontally into a three-dimensional plane.
On the other hand, in the related art lamp described in the JP-A-2003-59313, although the light emitted from the LED elements is formed into the parallel beam by the Fresnel lens, since the reflecting surface which is tilted relative to the parallel beam is made into the light emitting surface, the difference in optical path length between the portions near and far from the LED elements directly creates a difference in brightness over the reflecting surface. Therefore, there is a disadvantage in that it becomes difficult to obtain a uniform brightness on the light emitting surface. In addition, since the reflector has a reflecting surface that is approximately flat, the light emitting surface of the lamp is limited to a surface which is close to the two-dimensional surface, and therefore, as has been described before, there is a disadvantage in that the lamp described in JP-A-2003-59313 becomes difficult to be applied in a case where the light emitting surface is curved in a three-dimensional fashion.
Additionally, related art lamps which have a light guide plate as a light emitting unit disposed within a lamp housing of the lamp have been proposed. This light guide plate is plate-like shape and is made of transparent resin in which the light is introduced therein so as to be totally reflected on an internal surface thereof. The guide plate is disposed so that a surface having large square faces forward of the lamp as a light emission surface and a plurality of minute reflecting elements are provided on a rear surface of the light emission surface. The minute reflecting elements have conical or pyramidal minute recesses which are referred to as stipple. In addition, an end face of the light guide plate which lies orthogonal to the light emission surface is made into a light introduction surface, and a light source of LED elements or the like is arranged so as to be opposed to the light introduction surface. When light emitted from the LED elements is guided into the interior of the light guide plate through the light introduction surface, the light so guided is reflected by the minute reflecting elements so as to be emitted from the light emission surface. Such a related art lamp is described, for example, in Japanese Patent Unexamined Publication JP-A-2000-251508.
In the light emission unit described in JP-A-2000-251508, since a light guide plate is formed into a flat rectangular plate shape, light from LED elements which is inputted from an end face of the light guide plate is guided while traveling straight in an interior of the light guide plate. Total reflecting cuts are provided on a rear surface of the light guide plate. Since the light which is guided in the interior of the light guide plate is reflected by these total reflecting cuts so as to be emitted from a front surface of the light guide plate, the front surface of the light guide plate is configured as a light emitting surface. In addition, in JP-A-2000-251508, since light from the LED elements is made to be incident on end faces of four sides of the rectangular light guide plate, light can be guided to almost the whole areas of the light guide plate, whereby light can be emitted from the whole surface with almost uniform brightness.
In the related art lamp including a light guide plate emission unit like the one described above, there is a disadvantage in that mounting the light emission unit of the light guide plate within the lamp housing is difficult (i.e., it is difficult to form the light guide plate in a flat plate shape). Moreover, there is an additional disadvantage in that the number of LED elements that may be used are restricted (i.e., it is difficult to introduce the light of LED element from a certain end face of the light guide plate as described in the JP-A-2000-251508). In such cases, the light has to be introduced into the light guide plate from only part of the end faces of the light guide plate, and as this occurs, guiding light over the whole surface areas of the light guide plate becomes difficult. Thus, it becomes difficult to illuminate all the surfaces of the light guide plate with uniform brightness.
In particular, since there are many cases in which a front cover which is disposed at a front side of a lamp is formed into a curved surface to follow a body configuration of a vehicle, when a light emitting unit of the light guide plate is mounted in an interior of such a lamp, a light guide plate needs to be curved in two-dimensions or three-dimensions in accordance with the curvature of the front cover. In addition, in the event that the light guide plate is desired to be a shape other than a rectangular shape, there is a disadvantage in that light from the LED elements has to be guided into the light guide plate only from one of the end faces of the light guide plate. As this occurs, light that has been guided into the interior of the light guide plate leaks to the outside of the light guide plate at a portion where the light guide plate is curved two-dimensionally or three-dimensionally because the inner surface of the light guide plate at the two-or three-dimensionally curved portion does not have total reflection of light thereon. Accordingly, the light cannot be guided to areas of the light guide plate which lie further ahead, and the quantity of light emitted from the light emitting surfaces of those areas is reduced. Thus, the light guide plate cannot be illuminated with uniform brightness over the whole surface area thereof. Because of this, an uniform lighting state cannot be obtained in the related art lamp with the light guide plate in such a state when the lamp is seen from the front thereof, and therefore, the illumination effect of the lamp is reduced.